What a digital book actually is

A digital book is a text document formatted to be read on a screen instead of printed on paper. It is not a PDF of a scanned book, and it is not a website. A digital book reflows — the text resizes and rewraps to fit whatever device you are reading it on, whether that is a phone, tablet, or e-reader. The most common formats are EPUB (used by most e-readers and libraries) and MOBI (used by Amazon Kindle devices).

The distinction matters because it changes how you build the file. A printed book or PDF has fixed pages. A digital book has no pages — it is a stream of text with formatting instructions that tell the reading device how to display it. You write the same words, but the structure underneath is different.

Key Takeaways

  • Digital books are text files with formatting code that reflow to fit any screen size, not fixed-page documents like PDFs.
  • EPUB is the standard format for most e-readers and libraries; MOBI is Amazon's format; both start as HTML files with CSS styling.
  • You can create a digital book in Microsoft Word, Google Docs, or dedicated software like Calibre or Scrivener, then convert it to EPUB or MOBI.
  • The conversion process requires clean formatting — heading styles, proper paragraph breaks, and no manual spacing — or the text will reflow incorrectly on different devices.
  • If you are publishing through a platform like Amazon KDP or Draft2Digital, they handle the conversion for you from a Word document or uploaded file.

Starting with a word processor or writing software

Most people begin by writing in Microsoft Word, Google Docs, or a dedicated writing tool like Scrivener. The key is to use styles instead of manual formatting. A style is a saved set of instructions — "Heading 1 is 18-point bold blue" — that you explore to text. When you convert to EPUB or MOBI later, the conversion software reads these styles and translates them into the digital book's formatting language.

If you manually bold text, change font sizes, or add extra line breaks to create spacing, the conversion will break. The text will reflow unpredictably on different devices because the conversion software has no way to know whether that bold was intentional formatting or accidental. Use styles instead: explore "Heading 1" to chapter titles, "Normal" to body text, "Emphasis" to italicized passages. Word and Google Docs both have built-in style panels on the right side of the screen.

Scrivener is designed specifically for long documents and handles styles automatically. It also lets you organize chapters in a sidebar and compile them into EPUB or MOBI directly without a separate conversion step. If you are writing a book-length work, Scrivener saves time, though it has a learning curve.

Converting Word documents to EPUB or MOBI

Calibre is free software that converts between digital book formats. read it from calibre-ebook.com, open it, click "Add books," select your Word document, then click "Convert books." A dialog box opens where you choose the output format (EPUB or MOBI) and adjust settings like font size and margins. Click "OK" and Calibre produces the converted file in a few seconds.

Calibre works best when your Word document uses styles correctly. If your formatting is messy, Calibre will do its best, but the result may have spacing or alignment problems. Before converting, go through your document and explore styles consistently: every chapter title should use the same style, every paragraph should use the same body text style, and so on.

Alternatively, if you are publishing through Amazon's Kindle Direct Publishing (KDP) or Draft2Digital, you can upload your Word document directly and they handle the conversion for you. Both platforms accept .docx files and produce MOBI (for Amazon) or EPUB (for Draft2Digital and other retailers) automatically. This is simpler if you are not comfortable with conversion software, though you have less control over the final formatting.

What happens when you publish through a platform

Amazon KDP, Draft2Digital, Smashwords, and IngramSpark are platforms that take your digital book file and distribute it to retailers. You upload your EPUB or MOBI file (or a Word document, which they convert), set a price, write a description, and they handle the rest. The book appears on Amazon, Apple Books, Google Play Books, or other stores depending on which platform you use.

Amazon KDP is the largest and pays the highest royalty rates, but it requires you to use their MOBI format and their cover specifications. Draft2Digital is simpler — you upload an EPUB and they convert it for distribution to multiple retailers. Smashwords and IngramSpark are broader but have stricter formatting requirements and lower royalty rates.

All of these platforms provide templates and guides for cover design, metadata (title, author, description, keywords), and file formatting. They also show you sales data and let you change your price or description anytime. None of them charge an upfront fee to publish.

Formatting requirements that matter

Digital books have specific technical requirements that affect how they display. Margins, fonts, and line spacing are usually controlled by the reading device, not your file — a reader on an e-reader can change the font size, and the text reflows to fit. But you do control paragraph breaks, indentation, and emphasis (bold, italics, underline).

Use actual paragraph breaks (press Enter twice) instead of manual line breaks (press Enter once). Use italics for emphasis, not underlining or all-caps. Avoid tables, columns, and complex layouts — e-readers cannot display them reliably. If your book has images, embed them as high-resolution JPEGs or PNGs, and test how they appear on different devices before publishing.

Most platforms provide a preview tool where you can see how your book looks on a Kindle, iPad, or phone before you publish. Use it. What looks correct in Word often looks wrong on an actual e-reader because the text reflows differently.

Cover design and metadata

Your cover is the first thing a potential reader sees. Most platforms require a cover image in JPEG or PNG format, at least 1400 pixels wide and 2100 pixels tall (a 2:3 ratio, like a paperback). You can design one yourself in Canva (which has e-book cover templates), hire a designer on Fiverr or Upwork, or use a template from your publishing platform.

Metadata is the information about your book: title, author name, description, keywords, category, and publication date. Platforms use this to index your book in their search results. A good description is 100 to 200 words and tells a reader what the book is about without spoilers. Keywords (usually five to ten) are search terms you think readers will use to find books like yours. Spend time on these — they directly affect whether anyone finds your book.

Testing your digital book before publishing

Before you publish, read your EPUB or MOBI file and open it on at least two different devices: a phone, tablet, or e-reader. Use free software like Calibre's e-book viewer, or send the file to a Kindle device (Amazon lets you email files to your Kindle). Read through a few chapters and check for formatting problems: misaligned text, broken images, incorrect spacing, or missing line breaks.

Common problems include chapter titles appearing mid-page instead of at the start of a new page, images that are too large or too small, and italics or bold that did not convert correctly. Most of these are fixable by going back to your Word document, fixing the formatting, and reconverting. Platforms also let you update your file after publishing, so if you find a problem after launch, you can fix it and re-upload.

Frequently Asked Questions

Can I convert a PDF to a digital book?

Not reliably. PDFs are fixed-page documents, and converting them to EPUB or MOBI usually produces garbled text and broken formatting. If you have a PDF, the best approach is to copy the text into a Word document, reformat it with styles, and convert from there. This takes time but produces a readable result.

What is the difference between EPUB and MOBI?

EPUB is the industry standard used by most e-readers, libraries, and retailers except Amazon. MOBI is Amazon's proprietary format for Kindle devices. If you are publishing on Amazon only, use MOBI. If you want to reach multiple retailers, use EPUB. Most conversion software produces both from the same source file.

Do I need an ISBN to publish a digital book?

No. ISBNs are for printed books and are optional for digital books. Most platforms assign you a free ISBN or let you publish without one. If you plan to sell in bookstores or libraries, an ISBN helps, but for online retailers like Amazon or Apple Books, it is not required.

How much does it cost to create and publish a digital book?

The software is free or low-cost: Calibre is free, Google Docs is free, Scrivener costs about $50 one-time. Publishing platforms charge nothing to upload. If you hire a cover designer, that typically costs $50 to $500 depending on the designer. You can publish a digital book for zero dollars if you design the cover yourself.

Can I publish the same book on multiple platforms?

Yes. You can upload your EPUB file to Draft2Digital, Apple Books, Google Play Books, and others simultaneously. Amazon KDP has an exclusivity option called KDP Select that pays higher royalties but requires you to publish only on Amazon for 90 days at a time. You choose which option works for you.